Induced transmission filter

ABSTRACT

An optical filter may include a first group of layers. The first group of layers may include alternating layers of a first dielectric material, of a group of dielectric materials, and a second dielectric material of the group of dielectric materials. The optical filter may include a second group of layers. The second group of layers may include alternating layers of a third dielectric material, of the group of dielectric materials, and a fourth dielectric material of the group of dielectric materials. The optical filter may include a third group of layers. The third group of layers may include alternating layers of a fifth dielectric material, of the group of dielectric materials, a sixth dielectric material, of the group of dielectric materials, and a metal material. The third group of layers may be disposed between the first group of layers and the second group of layers.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/247,046, filed on Nov. 25, 2020 (now U.S. Pat. No. 11,340,391), whichis a continuation of U.S. patent application Ser. No. 16/591,849, filedon Oct. 3, 2019 (now U.S. Pat. No. 10,866,347), which is a continuationof U.S. patent application Ser. No. 15/601,773 (now U.S. Pat. No.10,451,783), filed on May 22, 2017, the contents of which areincorporated by reference herein in their entirety.

BACKGROUND

An optical sensor device may be utilized to capture information. Forexample, the optical sensor device may capture information relating to aset of electromagnetic frequencies. The optical sensor device mayinclude a set of sensor elements (e.g., optical sensors, spectralsensors, and/or image sensors) that capture the information. Forexample, an array of sensor elements may be utilized to captureinformation relating to multiple frequencies. In one example, an arrayof sensor elements may be utilized to capture information regarding aset of color bands of light, such as a first sensor element, of thesensor element array, capturing information regarding a red band oflight; a second sensor element, of the sensor element array, capturinginformation regarding a green band of light; a third sensor element, ofthe sensor element array, capturing information regarding a blue band oflight, or the like.

A sensor element, of the sensor element array, may be associated with afilter. The filter may include a passband associated with a firstspectral range of light that is passed to the sensor element. The filtermay be associated with blocking a second spectral range of light frombeing passed to the sensor element. In one example, a sensor elementarray may be associated with a filter including different colorpassbands, such as a red passband, a blue passband, a green passband, orthe like (e.g., a red-green-blue (RGB) filter). In other examples, asensor element array be associated with a near infrared (NIR) blockingfilter, an infrared (IR) blocking filter, a long wave pass (LWP) filter,a short wave pass (SWP) filter, a photopic filter, a tristimulus filter,or the like.

SUMMARY

According to some possible implementations, an optical filter mayinclude a first group of layers. The first group of layers may includealternating layers of a first dielectric material, of a group ofdielectric materials, and a second dielectric material of the group ofdielectric materials. The optical filter may include a second group oflayers. The second group of layers may include alternating layers of athird dielectric material, of the group of dielectric materials, and afourth dielectric material of the group of dielectric materials. Theoptical filter may include a third group of layers. The third group oflayers may include alternating layers of a fifth dielectric material, ofthe group of dielectric materials, a sixth dielectric material, of thegroup of dielectric materials, and a metal material. The third group oflayers may be disposed between the first group of layers and the secondgroup of layers.

According to some possible implementations, an induced transmissionfilter may include a first all-dielectric portion including a first setof dielectric layers. The induced transmission filter may include asecond all-dielectric portion including a second set of dielectriclayers. The induced transmission filter may include a metal/dielectricportion including a third set of dielectric layers and one or more metallayers. The metal/dielectric portion may be disposed between the firstall-dielectric portion and the second all-dielectric portion.

According to some possible implementations, a mixed metal/dielectricoptical filter may include a substrate. The mixed metal/dielectricoptical filter may include a first all-dielectric portion includingalternating silicon dioxide layers and niobium titanium oxide layers.The mixed metal/dielectric optical filter may include a secondall-dielectric portion including alternating silicon dioxide layers andniobium titanium oxide layers. The mixed metal/dielectric optical filtermay include a metal/dielectric portion including one or more layergroups. A layer group, of the one or more layer groups, may include asilver layer, two zinc oxide layers, and two niobium titanium oxidelayers. The silver layer may be disposed between the two zinc oxidelayers. The two zinc oxide layers may be disposed between the twoniobium titanium oxide layers. The metal/dielectric portion may bedisposed between the first all-dielectric portion and the secondall-dielectric portion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C are diagrams of an overview of an example implementationdescribed herein;

FIGS. 2A-2C are diagrams of characteristics of an all-dielectric opticalfilter described herein;

FIGS. 3A-3C are diagrams of characteristics of a low angle shift inducedtransmission optical filter (ITF) described herein;

FIGS. 4A-4C are diagrams of characteristics of a mixed metal/dielectricoptical filter described herein;

FIGS. 5A-5C are diagrams of characteristics of a mixed metal/dielectricoptical filter described herein;

FIGS. 6A and 6B are diagrams of characteristics of a set of opticalfilters described herein; and

FIGS. 7A-7G are diagrams of characteristics of a set of optical filtersdescribed herein.

DETAILED DESCRIPTION

The following detailed description of example implementations refers tothe accompanying drawings. The same reference numbers in differentdrawings may identify the same or similar elements.

An optical sensor device may include a sensor element array of sensorelements to receive light initiating from an optical source, such as anoptical transmitter, a light bulb, an ambient light source, or the like.The optical sensor device may utilize one or more sensor technologies,such as a complementary metal-oxide-semiconductor (CMOS) technology, acharge-coupled device (CCD) technology, or the like. A sensor element(e.g., an optical sensor), of the optical sensor device, may obtaininformation (e.g., spectral data) regarding a set of electromagneticfrequencies.

A sensor element may be associated with a filter that filters light tothe sensor element to enable the sensor element to obtain informationregarding a particular spectral range of electromagnetic frequencies.For example, the sensor element may be aligned with a red-green-blue(RGB) filter, a near infrared (NIR) blocking filter, an infrared (IR)blocking filter, a long wave pass (LWP) filter, a short wave pass (SWP)filter, a photopic filter, a tristimulus filter, or the like to cause aportion of light that is directed toward the sensor element to befiltered. A filter may include sets of dielectric layers to filter theportion of the light. For example, a filter may include dielectricfilter stacks of alternating high-index layers and low-index layers,such as alternating layers of niobium titanium oxide (NbTiO_(x)) andsilicon dioxide (SiO₂). However, all-dielectric types of filters may beassociated with a threshold angle shift at increasing angles ofincidence. For example, an all-dielectric filter may be associated withan angle shift of greater than approximately 10 nm at an angle ofincidence of 20 degrees, greater than approximately 20 nm at an angle ofincidence of 30 degrees, greater than approximately 40 nm at an angle ofincidence of 40 degrees, greater than approximately 50 nm at an angle ofincidence of 50 degrees, or the like.

A low angle shift (LAS) filter with alternating layers of high-indexdielectric, low-index dielectric, and metal may be selected to reduce anangle shift relative to an all-dielectric filter. For example, a lowangle shift filter may utilize layers of niobium titanium oxide, zincoxide, and silver to reduce an angle shift relative to an all-dielectricfilter. However, the low angle shift filter may be associated with atransmissivity in a passband of the low angle shift filter that does notsatisfy a threshold. For example, a low angle shift filter may beassociated with a transmissivity of less than approximately 70% at arange of angles of incidence from 0 degrees to 50 degrees.

Some implementations, described herein, provide a mixed dielectric/metalfilter with portions of alternating dielectric layers sandwiching aportion of dielectric layers and metal layers. For example, an opticalfilter may include a first portion with a set of alternating high-indexlayers of niobium titanium oxide and low-index layers of silicondioxide, a second portion with another set of alternating high-indexlayers of niobium titanium oxide and low-index layers of silicondioxide, and a third portion, disposed between the first portion and thesecond portion, of alternating layers of high-index layers of niobiumtitanium oxide, low-index layers of zinc oxide, and metal layers ofsilver. In this way, the filter may filter light with less than athreshold angle shift and with greater than a threshold level oftransmission. For example, a mixed dielectric/metal filter may beassociated with an angle shift of less than approximately 30 nm atangles of incidence from 0 degrees to 50 degrees, an angle shift of lessthan approximately 20 nm at angles of incidence from 0 degrees to 40degrees, an angle shift of less than approximately 10 nm at angles ofincidence from 0 degrees to 20 degrees, or the like. Similarly, a mixeddielectric/metal filter may be associated with a transmissivity ofgreater than approximately 70% at angles of incidence from 0 degrees to50 degrees, greater than approximately 75% at angles of incidence from 0degrees to 50 degrees, or the like.

FIGS. 1A-1C are a diagrams of an overview of example implementations100/100′/100″ described herein. As shown in FIG. 1A, exampleimplementation 100 includes a sensor system 110. Sensor system 110 maybe a portion of an optical system, and may provide an electrical outputcorresponding to a sensor determination. Sensor system 110 includes anoptical filter structure 120, which includes an optical filter 130, andan optical sensor 140. For example, optical filter structure 120 mayinclude an optical filter 130 that performs a passband filteringfunctionality. In another example, an optical filter 130 may be alignedto an array of sensor elements of optical sensor 140.

Although implementations, described herein, may be described in terms ofan optical filter in a sensor system, implementations described hereinmay be used in another type of system, may be used external to a sensorsystem, or the like.

As further shown in FIG. 1A, and by reference number 150, an inputoptical signal is directed toward optical filter structure 120. Theinput optical signal may include but is not limited to visible spectrum(VIS) and NIR light (e.g., ambient light from the environment in whichsensor system 110 is being utilized). In another example, the opticaltransmitter may direct another spectral range of light for anotherfunctionality, such as a testing functionality, a measurementfunctionality, a communications functionality, or the like.

As further shown in FIG. 1A, and by reference number 160, a firstportion of the optical signal with a first spectral range is not passedthrough by optical filter 130 and optical filter structure 120. Forexample, dielectric filter stacks, which may include high-index materiallayers and low-index material layers, and silver/dielectric filterstacks of optical filter 130, may cause the first portion of light to bereflected in a first direction, to be absorbed, or the like. As shown byreference number 170, a second portion of the optical signal is passedthrough by optical filter 130 and optical filter structure 120. Forexample, optical filter 130 may pass through the second portion of lightwith a second spectral range in a second direction toward optical sensor140.

As further shown in FIG. 1A, and by reference number 180, based on thesecond portion of the optical signal being passed to optical sensor 140,optical sensor 140 may provide an output electrical signal for sensorsystem 110, such as for use in imaging, ambient light sensing, detectingthe presence of an object, performing a measurement, facilitatingcommunication, or the like. In some implementations, another arrangementof optical filter 130 and optical sensor 140 may be utilized. Forexample, rather than passing the second portion of the optical signalcollinearly with the input optical signal, optical filter 130 may directthe second portion of the optical signal in another direction toward adifferently located optical sensor 140.

As shown in FIG. 1B, a similar example implementation 100′ includes aset of sensor elements of a sensor element array 140 is integrated intoa substrate 120 of an optical filter structure. In this case, opticalfilter 130 is disposed onto substrate 120. Input optical signals 150-1and 150-2 are received at a set of angles and a first portion of inputoptical signals 150-1 and 150-2 is reflected at another set of angles.In this case, a second portion of input optical signals 150-1 and 150-2is passed through optical filter 130 to sensor element array 140, whichprovides an output electrical signal 180.

As shown in FIG. 1C, another similar example implementation 100″includes a set of sensor elements of a sensor element array 140separated from an optical filter structure 120, and optical filter 130is disposed onto optical filter structure 130. In this case, opticalfilter structure 130 and sensor element array 140 may be separated byfree space or the like. Input optical signals 150-1 and 150-2 arereceived at a set of angles at optical filter 130. A first portion 160of the input optical signals 150-1 and 150-2 is reflected and a secondportion 170 is passed by optical filter 130 and optical filter structure120 to sensor element array 140, which provides an output electricalsignal 180.

As indicated above, FIGS. 1A-1C are provided merely as examples. Otherexamples are possible and may differ from what was described with regardto FIGS. 1A-1C.

FIGS. 2A-2C are diagrams of characteristics relating to an opticalfilter. FIGS. 2A-2C show an example of an all-dielectric filter.

As shown in FIG. 2A, and by chart 200, a filter 210 may include asubstrate and a set of dielectric stacks. The substrate may include asilicon nitride (Si₃N₄ and shown as Si₃N₄), a glass substrate, a polymersubstrate, another transparent substrate, or the like. In someimplementations, the substrate may be attached to the set of dielectricstacks using an epoxy (e.g., a transparent glue), an air gap (e.g., withan epoxy outside of an optical path), or the like. Additionally, oralternatively, the set of dielectric stacks may be disposed directlyonto a detector, detector array, sensor element array, or the like,which may form the substrate for the set of dielectric stacks. Forexample, a sensor element array may include a top layer of siliconnitride to which the set of dielectric stacks may be attached. Inanother example, such as for a back-illuminated detector, another typeof substrate may be used, such as a silicon substrate. In someimplementations, the substrate may be an entrance medium, an exitmedium, or the like for the set of dielectric stacks. The set ofdielectric stacks includes alternating layers of niobium titanium oxide(NbTiO₅ and shown as NbTiO₅) and silicon dioxide (SiO₂ and shown asSiO2). For example, filter 210 may include a first niobium titaniumoxide layer with a thickness of 99.8 nanometers (nm) deposited onto thesubstrate and a first silicon dioxide layer with a thickness of 172.1 nmdeposited onto the niobium titanium oxide layer. Similarly, filter 210may include a second niobium titanium oxide layer deposited with athickness of 105.2 nm deposited onto the first silicon dioxide layer anda second silicon dioxide layer with a thickness of 180.5 nm depositedonto the second niobium titanium oxide layer. In this case, filter 210is associated with a total thickness of approximately 5.36 micrometers(μm), which may result in excessive deposition time and excessive costrelating to the increased deposition time. Moreover, the total thicknessmay result in a threshold amount of compressive stress, which may resultin a warping of a substrate with less than a threshold thickness andwhich may result in excessive difficulty and yield loss when portioninga substrate onto which multiple filters are deposited to form multiple,discrete filters.

As shown in FIG. 2B, and by chart 220, a filter response for filter 210exposed to an exit medium of air is provided. For example, filter 210 isassociated with a cut-off wavelength (e.g., a wavelength at which atransmissivity of filter 210 reduces at a threshold rate) ofapproximately 660 nm at an angle of incidence (AOI) of 0 degrees. Incontrast, at angles of incidence of 10 degrees, 20 degrees, 30 degrees,40 degrees, and 50 degrees, filter 210 is associated with a thresholdshift in the cut-off wavelength of approximately 5 nm, approximately 12nm, approximately 25 nm, approximately 42 nm, and approximately 52 nm,respectively. Moreover, for angles of incidence of 30 degrees, 40degrees, and 50 degrees, filter 210 is associated with atransmissivities of approximately 4% at approximately 880 nm,approximately 31% at approximately at approximately 850 nm, andapproximately 14% at approximately 805 nm, respectively. Furthermore,filter 210 is associated with a drop in transmissivity to below athreshold transmissivity (e.g., to a transmissivity of betweenapproximately 58% and approximately 68%) between approximately 480 nmand approximately 505 nm at an AOI of 50 degrees, and filter 210 isassociated with an increase in transmissivity to greater than athreshold transmissivity (e.g., to a transmissivity greater thanapproximately 1%) at a spectral range greater than approximately 1000 nmfor the AOI of 50 degrees. For a usage of filter 210 to provide apassband between approximately 420 nm and approximately 620 nm, thethreshold angle shifts and the threshold transmissivity drops andincreases result in relatively poor filter performance.

As shown in FIG. 2C, and by chart 230, a color plot for filter 210 isprovided (e.g., an International Commission on Illumination (CIE) 1931color plot). As shown by reference number 232, filter 210 is associatedwith a CIE color plot indicating a threshold color shift betweenapproximately (0.33, 0.33) to approximately (0.30, 0.33) at a shift froma 0 degree AOI to a 50 degree AOI. The threshold color shift results inrelatively poor filter performance.

As indicated above, FIGS. 2A-2C are provided merely as examples. Otherexamples are possible and may differ from what was described with regardto FIGS. 2A-2C.

FIGS. 3A-3C are diagrams of characteristics relating to an opticalfilter. FIGS. 3A-3C show an example of a low angle shift inducedtransmission optical filter (ITF) with dielectric/metal filter stacks.

As shown in FIG. 3A, and by chart 300, a filter 310 may include asubstrate, a set of dielectric layers, and a set of metal layers. Thesubstrate may include a silicon nitride substrate. The set of dielectriclayers and the set of metal layers include alternating layers of niobiumtitanium oxide, zinc oxide (ZnO), and silver (Ag). For example, a firstlayer of niobium titanium oxide with a thickness of 28.0 nm is depositedonto a silicon nitride substrate, a second layer of zinc oxide with athickness of 2.0 nm is deposited onto the first layer, a third layer ofsilver with a thickness of 11.3 nm is deposited onto the second layer, afourth layer of zinc oxide with a thickness of 2.0 nm is deposited ontothe third layer, and a fifth layer of niobium titanium oxide with athickness of 53.8 nm is deposited onto the fourth layer. In this case,the fifth layer of niobium titanium oxide may be multiple layers ofniobium titanium oxide. In other words, a first portion of the fifthlayer may be to sandwich the second layer through the fourth layer withthe first layer, and a second portion of the fifth layer may be tosandwich a sixth layer through an eighth layer with a portion of a ninthlayer. Although filter 310 is described with a particular set of layerthicknesses, other layer thicknesses are possible and may differ fromwhat is shown in FIG. 3A.

As shown in FIG. 3B, and by chart 320, a filter response for filter 310exposed to an exit medium of air is provided. As shown by referencenumber 322, filter 310 is associated with a reduced angle shift relativeto filter 210. For example, filter 310 is associated with an angle shiftof a cutoff wavelength of less than approximately 20 nm for a change inangle of incidence from 0 degrees to 10 degrees, 20 degrees, 30 degrees,40 degrees, or 50 degrees compared with an angle shift of great than 20nm for a change in angle of incidence from 0 degrees to 30 degrees, 40degrees, or 50 degrees. However, as shown by reference number 324,filter 310 is associated with a reduced transmissivity relative tofilter 210. For example, filter 310 is associated with an averagetransmissivity of between approximately 62% and 65% for angles ofincidence between 0 degrees and 50 degrees in a spectral range of thepassband of between approximately 420 nm and approximately 620 nm. Inthis case, a transmissivity in an infrared (IR) blocking spectral rangeof approximately 750 nm to approximately 1100 nm is approximately 0.41%for an AOI of 0 degrees and approximately 0.37% for an AOI of 40degrees.

As shown in FIG. 3C, and by chart 330, a CIE 1931 color plot of filter310 is provided. As shown by reference number 332, filter 310 isassociated with a reduced color shift relative to filter 210 for a shiftfrom a 0 degree angle of incidence to a 50 degree angle of incidence.For example, filter 310 is associated with a color shift less than athreshold (e.g., less than 0.2, less than 0.1, less than 0.05, etc.).

As indicated above, FIGS. 3A-3C are provided merely as examples. Otherexamples are possible and may differ from what was described with regardto FIGS. 3A-3C.

FIGS. 4A-4C are a diagram of characteristics relating to a mixedmetal/dielectric optical filter. FIGS. 4A-4C show an example of anoptical filter with dielectric filter stacks of high-index layers andlow-index layers and with a metal (e.g., silver) dielectric filter stackdisposed between the dielectric filter stacks.

As shown in FIG. 4A, and by chart 400, a filter 410 may include asubstrate, a set of dielectric layers, and a set of metal layers. Asshown by reference number 412, a first portion of filter 410 (e.g., afirst all-dielectric portion) includes all-dielectric layers ofalternating high-index layers and low-index layers. In this case, thealternating high-index layers and low-index layers are, respectively,niobium titanium oxide layers and silicon dioxide layers. For example, afirst layer deposited onto the silicon nitride substrate is a niobiumtitanium oxide layer with a thickness of 95.5 nm (shown as layer 1), asecond layer deposited onto the first layer is silicon dioxide with athickness of 48.3 nm (shown as layer 2), etc. In some implementations,another type of substrate may be used, such as a glass substrate or thelike. In some implementations, another high-index material may be used,such as a material with a refractive index greater than approximately2.0, greater than approximately 2.5, greater than approximately 3.0,greater than approximately 3.5, greater than approximately 3.6, greaterthan approximately 3.7, etc. In some implementations, another low-indexmaterial may be used, such as a material with a refractive index lessthan approximately 3.0, less than approximately 2.5, less thanapproximately 2.0, less than approximately 1.5, etc. In someimplementations, one or more layers may utilize, as a dielectricmaterial, an oxide material, such as silicon dioxide (SiO₂), niobiumpentoxide (Nb₂O₅), tantalum pentoxide (Ta₂O₅), titanium dioxide (TiO₂),aluminum oxide (Al₂O₃), zirconium oxide (ZrO₂), yttrium oxide (Y₂O₃),hafnium dioxide (HfO₂), or the like; a nitride material, such as siliconnitride (Si₃N₄); a fluoride material, such as magnesium fluoride (MgF);a sulfide material, such as zinc sulfide (ZnS); a selenide material,such as zinc selenide (ZnSe); a hydrogenated material, such ashydrogenated silicon or hydrogenated germanium; a nitrogenated material,such as nitrogenated germanium; a combination thereof; or the like.

As further shown in FIG. 4A, and by reference number 414, a secondportion of filter 410 includes mixed metal/dielectric layers. In thiscase, the second portion of filter 410 includes multiple layer groups ofone or more niobium titanium oxide layers, one or more zinc oxidelayers, and one or more silver layers. For example, a first layer group(layers 7 to 11) includes a layer of niobium titanium oxide with athickness of 139.1 nm (e.g., shown as layer 7, a first portion of whichmay be a part of the first portion of filter 410 and a second portion ofwhich may be a part of the second portion of filter 410), a layer ofzinc oxide with a thickness of 2.0 nm (shown as layer 8), a layer ofsilver with a thickness of 9.9 nm (shown as layer 9), a layer of zincoxide with a thickness of 2.0 nm (shown as layer 10), and a layer ofniobium titanium oxide with a thickness of 51.9 nm (shown as layer 11, afirst portion of which may be a part of the first layer group, a secondportion of which may be a part of a second layer group). Further to theexample, a second layer group (layers 11 to 15), includes the secondportion of layer 11 of niobium titanium oxide, layer 12 of zinc oxide,layer 13 of silver, layer 14 of zinc oxide, and a first portion of layer15 of niobium titanium oxide (e.g., a second portion of which may bepart of a third layer group). In another example, another metal materialmay be utilized.

As further shown in FIG. 4A, and by reference number 416, a thirdportion of filter 410 (e.g., a second all-dielectric portion) includesall-dielectric layers of alternating high-index layers and low-indexlayers. In this case, the alternating high-index layers and low-indexlayers are, respectively, niobium titanium oxide layers and silicondioxide layers. For example, a first layer is a portion of layer 23 ofniobium titanium oxide, a second layer is layer 24 of silicon dioxide, athird layer is layer 25 of niobium titanium oxide, a fourth layer islayer 26 of silicon dioxide, etc. In this case, filter 410 utilizesthree different dielectric materials. In another example, filter 410 mayutilize two different dielectric materials. In some implementations,filter 410 may be matched to an exit medium of air. In someimplementations, filter 410 may be matched to another exit medium, suchas a polymer material, a color dye, an RGB dye, an epoxy material, aglass material, or the like. In some implementations, filter 410 may bean RGB filter (e.g., a filter with a passband corresponding to a redspectral range of light, a green spectral range of light, or a bluespectral range of light), an NIR blocker, an LWP filter, an SWP filter,a photopic filter, an ambient light sensor filter, a tri-stimulusfilter, or the like. Although filter 410 is described with a particularset of layer thicknesses, other layer thicknesses are possible and maydiffer from what is shown in FIG. 4A.

As shown in FIG. 4B, and by chart 420; and in FIG. 4C, and by chart 430,filter 410 is associated with a reduced angle shift and color shiftrelative to filter 210 and an improved transmissivity relative to filter310. For example, as shown by reference number 432 in FIG. 4B, filter410 is associated with a transitivity of approximately 80% atapproximately 420 nm and an angle of incidence of 0 degrees, and isassociated with a transmissivity greater than 70% for a spectral rangeof between approximately 420 nm and 550 nm for angles of incidence ofbetween 0 degrees and 50 degrees. Similarly, as shown by referencenumber 434 in FIG. 4B, filter 410 is associated with an angle shift ofless than approximately 40 nm for the spectral range of betweenapproximately 400 nm and approximately 1100 nm and angles of incidencebetween 0 degrees and 50 degrees.

As shown in FIG. 4C, and by chart 430, a CIE 1931 color plot of filter310 is provided. As shown by reference number 436, filter 410 isassociated with a reduced color shift relative to filter 210 for a shiftfrom a 0 degree angle of incidence to a 50 degree angle of incidence.For example, filter 410 is associated with a color shift less than athreshold (e.g., less than 0.2, less than 0.1, less than 0.05, etc.).

As indicated above, FIGS. 4A-4C are provided merely as examples. Otherexamples are possible and may differ from what was described with regardto FIGS. 4A-4C.

FIGS. 5A-5C are a diagram of characteristics relating to another mixedmetal/dielectric optical filter. FIGS. 5A-5C show another example of aninduced transmission optical filter with dielectric filter stacks ofhigh-index layers and low-index layers and with metal (e.g., silver)dielectric filter stacks.

As shown in FIG. 5A, and by chart 500, a filter 510 may include asubstrate, a set of dielectric layers, and a set of metal layers. Asshown by reference number 512, a first portion of filter 510, of layers1 to 10, includes all-dielectric layers of alternating high-index layersand low-index layers. In this case, the alternating high-index layersand low-index layers are, respectively, niobium titanium oxide layersand silicon dioxide layers. As shown by reference number 514, a secondportion of filter 510, of layers 10 to 25, includes metal dielectriclayers. In this case, the second portion of filter 510 includes multiplelayer groups of one or more niobium titanium oxide layers, one or morezinc oxide layers, and one or more silver layers. As shown by referencenumber 516, a third portion of filter 510, of layers 25 to 30, includesall-dielectric layers of alternating high-index layers and low-indexlayers. In this case, the alternating high-index layers and low-indexlayers are, respectively, niobium titanium oxide layers and silicondioxide layers. Although filter 510 is described with a particular setof layer thicknesses, other layer thicknesses are possible and maydiffer from what is shown in FIG. 5A.

As shown in FIG. 5B, and by chart 520; and in FIG. 5C, and by chart 530,filter 510 is associated with a reduced angle shift and color shiftrelative to filter 210 and an improved transmissivity relative to filter310. For example, as shown by reference number 532 in FIG. 5B, filter510 is associated with a transitivity of approximately 80% atapproximately 500 nm and at angles of incidence of 0 degrees to 50degrees, and is associated with a transmissivity greater thanapproximately 70% for a spectral range of between approximately 460 nmand 590 nm at angles of incidence between 0 degrees and 50 degrees.Similarly, as shown by reference number 534, filter 510 is associatedwith an angle shift of less than approximately 30 nm for the spectralrange of between approximately 400 nm and approximately 1100 nm andangles of incidence between 0 degrees and 50 degrees.

As shown in FIG. 5C, and by chart 530, a CIE 1931 color plot of filter510 is provided. As shown by reference number 536, filter 510 isassociated with a reduced color shift relative to filter 210 for a shiftfrom a 0 degree angle of incidence to a 50 degree angle of incidence.For example, filter 510 is associated with a color shift less than athreshold (e.g., less than 0.2, less than 0.1, less than 0.05, etc.).

As indicated above, FIGS. 5A-5C are provided merely as examples. Otherexamples are possible and may differ from what was described with regardto FIGS. 5A-5C.

FIGS. 6A and 6B are diagrams of characteristics relating to a set ofoptical filters. FIGS. 6A and 6B show a comparison of characteristics offilters described herein.

As shown in FIG. 6A, and by chart 600, a comparison of angle shifts ofthe cut-off wavelength for filter 210, filter 310, filter 410, andfilter 510 is provided. In this case, filter 410 and filter 510 areassociated with a reduced angle shift of the cut-off wavelength relativeto filter 210 at each angle of incidence from 0 degrees to 50 degrees.For example, at an angle of incidence of 40 degrees, filter 410 isassociated with an angle shift of a cut-off wavelength of approximately18 nm. Similarly, at an angle of incidence of 40 degrees, filter 510 isassociated with an angle shift of a cut-off wavelength of approximately20 nm. In contrast, at an angle of incidence of 20 degrees, filter 210is associated with a change in a cut-off wavelength of approximately 42nm.

As shown in FIG. 6B, and by chart 610, a comparison of averagetransmissivity of a passband of a spectral range of approximately 420 nmto approximately 620 nm for filter 210, filter 310, filter 410, andfilter 510 is provided. In this case, filter 410 and filter 510 areassociated with an improved transmissivity relative to filter 310. Ateach angle of incidence from 0 degrees to 50 degrees. For example, at anangle of incidence of 40 degrees, filter 410 and filter 510 areassociated with an average transmissivity of approximately 72% andapproximately 75%, respectively. In contrast, at an angle of incidenceof 40 degrees, filter 310 is associated with an average transmissivityof approximately 63%.

As indicated above, FIGS. 6A and 6B are provided merely as examples.Other examples are possible and may differ from what was described withregard to FIGS. 6A and 6B.

FIGS. 7A-7G are diagrams of characteristics relating to a set of opticalfilters. FIGS. 7A-7G show a comparison of characteristics of green colortypes of filters described herein.

As shown in FIG. 7A, an example stackup for a filter 702 is provided.Filter 702 may be a green color filter that includes alternating layersof silicon dioxide (SiO₂) and niobium titanium oxide (NbTiO₅). Filter702 may be associated with an entrance medium of silicon nitride (Si₃N₄)and an exit medium of air. Filter 702 may be an all-dielectric type offilter, and may be similar to filter 210, shown in FIG. 2A.

As shown in FIG. 7B, an example stackup for a filter 704 is provided.Filter 704 may be a green color filter that includes layers of niobiumtitanium oxide (NbTiO₅), zinc oxide (ZnO), and silver (Ag), an entrancemedium of silicon nitride (Si₃N₄), and an exit medium of air. Filter 704may be similar to filter 310, shown in FIG. 3A.

As shown in FIG. 7C, an example stackup for a filter 706 is provided.Filter 706 may be a green color filter that includes layers of niobiumtitanium oxide (NbTiO₅), silicon dioxide (SiO₂), zinc oxide (ZnO), andsilver (Ag), an entrance medium of silicon nitride (Si₃N₄), and an exitmedium of air. Filter 706 may be similar to filter 410 shown in FIG. 4A.For example, filter 706 may include a first portion, such as layers 1through 13, that includes alternating dielectric layers; a secondportion, such as layers 13 to 25, that includes alternating dielectriclayers and metal layers; and a third portion, such as layers 25 to 37,that includes alternating dielectric layers.

As shown in FIG. 7D, and by charts 708 and 710, a filter response forfilter 702 is provided. For example, filter 702 is associated with anangle shift for a change in angle of incidence (AOI) from approximately0 degrees to approximately 50 degrees of between approximately 50 nm andapproximately 80 nm for a spectral range of between approximately 450 nmand approximately 575 nm. Moreover, filter 702 is associated with a dropin peak transmission in a passband from approximately 100% at an angleof incidence of approximately 0 degrees to approximately 90% at an angleof incidence of approximately 50 degrees. Furthermore, filter 702 isassociated with a color shift in a CIE 1931 color plot fromapproximately [0.08, 0.47] to approximately [0.25, 0.69].

As shown in FIG. 7E, and by charts 712 and 714, a filter response forfilter 704 is provided. For example, filter 704 is associated with anangle shift for a change in angle of incidence (AOI) from approximately0 degrees to approximately 50 degrees of between approximately 25 nm andapproximately 40 nm for a spectral range of between approximately 450 nmand approximately 575 nm. Moreover, filter 704 is associated with a dropin peak transmission in a passband from approximately 72% at an angle ofincidence of approximately 0 degrees to approximately 66% at an angle ofincidence of approximately 50 degrees. Furthermore, filter 704 isassociated with a color shift in a CIE 1931 color plot fromapproximately [0.17, 0.58] to approximately [0.26, 0.63].

As shown in FIG. 7F, and by charts 716 and 718, a filter response forfilter 706 is provided. For example, filter 706 is associated with anangle shift for a change in angle of incidence (AOI) from approximately0 degrees to approximately 50 degrees of between approximately 25 nm andapproximately 40 nm for a spectral range of between approximately 450 nmand approximately 575 nm. Moreover, filter 706 is associated with a dropin peak transmission in a passband from approximately 78% at an angle ofincidence of approximately 0 degrees to approximately 70% at an angle ofincidence of approximately 50 degrees. Furthermore, filter 706 isassociated with a color shift in a CIE 1931 color plot fromapproximately [0.18, 0.62] to approximately [0.26, 0.65]. In this way,filter 706 is associated with a reduced angle shift and a reduced colorshift relative to filter 702 and an improved transmissivity relative tofilter 704.

As shown in FIG. 7G, and by charts 720 and 722, a comparison of changein center wavelength and a comparison in average transmission in apassband of approximately 510 nm to approximately 550 is provided,respectively, for filter 702, filter 704, and filter 706. As shown inchart 720, filter 706 is associated with a reduced change in centerwavelength relative to filter 702 for angles of incidence ofapproximately 10 degrees to approximately 50 degrees. As shown in chart722, filter 706 is associated with an improved average transmission, inthe passband, relative to filter 704 for angles of incidence ofapproximately 0 degrees to approximately 50 degrees, and an improvedaverage transmission relative to filter 706 for angles of incidence, inthe passband, from approximately 40 degrees to approximately 50 degrees.

As indicated above, FIGS. 7A-7G are provided merely as examples. Otherexamples are possible and may differ from what was described with regardto FIGS. 7A-7G.

In this way, utilization of a filter that includes a first portion ofdielectric layers, a second portion of mixed dielectric and metallayers, and a third portion of dielectric layers provides filtering witha reduced angle shift and improved transmissivity relative to anall-dielectric filter or LAS ITF filter. Based on reducing an angleshift and improving a transmissivity, an accuracy of data obtained by asensor element aligned to the filter is improved relative to an accuracyof data obtained by a sensor element aligned to another type of filter.

The foregoing disclosure provides illustration and description, but isnot intended to be exhaustive or to limit the implementations to theprecise form disclosed. Modifications and variations are possible inlight of the above disclosure or may be acquired from practice of theimplementations.

Some implementations are described herein in connection with thresholds.As used herein, satisfying a threshold may refer to a value beinggreater than the threshold, more than the threshold, higher than thethreshold, greater than or equal to the threshold, less than thethreshold, fewer than the threshold, lower than the threshold, less thanor equal to the threshold, equal to the threshold, etc.

Even though particular combinations of features are recited in theclaims and/or disclosed in the specification, these combinations are notintended to limit the disclosure of possible implementations. In fact,many of these features may be combined in ways not specifically recitedin the claims and/or disclosed in the specification. Although eachdependent claim listed below may directly depend on only one claim, thedisclosure of possible implementations includes each dependent claim incombination with every other claim in the claim set.

No element, act, or instruction used herein should be construed ascritical or essential unless explicitly described as such. Also, as usedherein, the articles “a” and “an” are intended to include one or moreitems, and may be used interchangeably with “one or more.” Furthermore,as used herein, the term “set” is intended to include one or more items(e.g., related items, unrelated items, a combination of related items,and unrelated items, etc.), and may be used interchangeably with “one ormore.” Where only one item is intended, the term “one” or similarlanguage is used. Also, as used herein, the terms “has,” “have,”“having,” or the like are intended to be open-ended terms. Further, thephrase “based on” is intended to mean “based, at least in part, on”unless explicitly stated otherwise.

What is claimed is:
 1. A filter comprising: a first plurality of layerscomprising dielectric layers; and a second plurality of layerscomprising metal layers, wherein the filter is associated with a drop inpeak transmission in a passband from approximately 78% at an angle ofincidence of approximately 0 degrees to approximately 70% at an angle ofincidence of approximately 50 degrees.
 2. The filter of claim 1, whereinthe filter is associated with an angle shift for a change in angle ofincidence from approximately 0 degrees to approximately 50 degrees for aspectral range of between approximately 450 nanometers (nm) andapproximately 575 nm.
 3. The filter of claim 2, wherein the filter isassociated with the angle shift for the change in AOI from approximately0 degrees to approximately 50 degrees for a spectral range of betweenapproximately 25 nm and approximately 40 nm.
 4. The filter of claim 1,wherein the second plurality of layers further comprise additionaldielectric layers that alternate with the metal layers.
 5. The filter ofclaim 1, wherein the dielectric layers are first alternating dielectriclayers, and wherein the filter further comprises: a third plurality oflayers comprising second alternating dielectric layers.
 6. The filter ofclaim 1, further comprising: an entrance medium of silicon nitride(Si₃N₄).
 7. The filter of claim 1, wherein the dielectric layers includealternating layers of niobium titanium oxide (NbTiO₅) and silicondioxide (SiO₂).
 8. The filter of claim 1, wherein the filter is furtherassociated with a color shift in an International Commission onIllumination (CIE) color plot from approximately [0.18, 0.62] toapproximately [0.26, 0.65].
 9. The filter of claim 1, wherein the filteris further associated with a color shift in an International Commissionon Illumination (CIE) 1931 color plot.
 10. A filter comprising: a firstportion that includes first dielectric layers alternating with seconddielectric layers; and a second portion that includes third dielectriclayers alternating with metal layers, wherein the filter is furtherassociated with a color shift in an International Commission onIllumination (CIE) color plot from approximately [0.18, 0.62] toapproximately [0.26, 0.65].
 11. The filter of claim 10, where the CIEcolor plot is a CIE 1931 color plot.
 12. The filter of claim 10, whereinthe filter is further associated with an angle shift for a change inangle of incidence (AOI) from approximately 0 degrees to approximately50 degrees for a spectral range of between approximately 450 nm andapproximately 575 nm.
 13. The filter of claim 10, wherein the filter isfurther associated with a drop in peak transmission in a passband fromapproximately 78% at an angle of incidence of approximately 0 degrees toapproximately 70% at an angle of incidence of approximately 50 degrees.14. The filter of claim 10, wherein the first dielectric layers compriselayers of niobium titanium oxide (NbTiO₅), and wherein the seconddielectric layers comprise layers of silicon dioxide (SiO₂).
 15. Thefilter of claim 10, wherein the third dielectric layers comprise zincoxide (ZnO), and wherein the metal layers comprise layers of silver(Ag).
 16. The filter of claim 10, further comprising: a third portionthat includes fourth dielectric layers alternating with fifth dielectriclayers, wherein the second portion is between the first portion and thethird portion.
 17. The filter of claim 16, wherein a material of thefirst dielectric layers is same as a material of the fourth dielectriclayers, and wherein a material of the second dielectric layers is sameas a material of the fifth dielectric layers.
 18. A filter comprising: afirst portion that includes first dielectric layers; a second portionthat includes second dielectric layers alternating with metal layers;and a third portion that includes third dielectric layers, wherein thesecond portion is between the first portion and the third portion, andwherein the filter is associated with a drop in peak transmission in apassband from approximately 78% to approximately 70%.
 19. The filter ofclaim 18, wherein the drop in peak transmission is approximately 78% atan angle of incidence of approximately 0 degrees.
 20. The filter ofclaim 18, wherein the drop in peak transmission is approximately 70% atan angle of incidence of approximately 50 degrees.